Even though it’s been four years since the devastating diamondback moth (DBM) outbreak, apprehension remains that DBM could appear in large numbers this fall.   In the desert, DBM is generally considered a minor pest that occasionally builds up to damaging levels in the late winter and spring. In fall produce crops, survey data has shown that DBMs can easily be controlled control with 1-2 well timed insecticide sprays.   But in the fall 2016, outbreaks of DBM population occurred throughout all vegetable growing regions in Arizona where it was determined that the source of the DBM originated from infested transplants.  We later discovered that the invasive DBM population was highly resistant to chlorantraniliprole (Coragen, Beseige, Belt and Vetica). Infestations experienced by Arizona growers that season were not anticipated, and overall, the resistant DBM caused serious economic losses in Cole crops.  However, the population abundance of DBM in the desert the last three seasons has been significantly lower than what was observed in 2016.   We have received no complaints from PCAs or growers of uncontrollable DBM infestations, crop damage or yield losses since 2016, and PCAs reported having no difficulty controlling larvae or adults with commonly used insecticides, including the chlorantraniliprole. In 2019, fall field inspections of transplants also yielded no larvae on plants arriving from local and coastal nurseries.  Thus, we have concluded that the DBM populations that appeared in in the desert in 2017, 2018 and 2019 were a distinctly different population than those that infested crops in the fall of 2016. It is highly likely that the DBM populations showing up in the desert the past 3 seasons migrated concurrently onto both direct-seeded and transplanted cole crops in wind currents following September storms. Field trials conducted at the Yuma Ag Center last year confirmed the local DBM populations were susceptible to the key insecticides (Radiant, Proclaim, pyrethroids, Verimark/Exirel, Coragen/Beseige) used for their management. In addition, laboratory bioassays of field collected DBM from YAC last fall and spring showed no indication of resistance to chlorantraniliprole.

In an attempt to document the impact of the DBM outbreaks on Arizona Cole crops the past four seasons, we conducted a two-part survey of growers and PCAs from Yuma, Maricopa and Imperial Counties in April 2019 to (1) estimate the severity of yield losses from DBM on direct-seeded and transplanted Cole crops, and (2) the intensity of chemical management required to control DBM, and associated level of control provided by each insecticide product used.  To download a copy of the survey results and recent research click on the following link: Survey of Diamondback Moth on Desert Cole Crops, 2016-2020

Note:   DBM are like a box of chocolates: “You never know what you’re going to get”.  Do not become complacent.  Because DBM populations disappear from the desert each summer and reappear on fall crops from outside sources (see graph below), we never really know how abundant fall populations will be, or how susceptible to insecticides they will be. So be vigilant in scouting and follow IPM guidelines for DBM management.  To download a copy of the 2020 DBM Management Guidelines, click on the following link: 2020 Guidelines for Diamondback Moth Management in Desert Cole Crops

 

 

Name that Pest – Aug 19, 2020

Please provide the common and scientific name for this insect.

When we go to the field to evaluate a crop, there are typically three fundamental points we need to take into consideration that include: 1) stage of growth, 2) general crop vigor and yield potential, and 3) anticipate the next stage of development and what we need to do in terms of field crop management.  These considerations are commonly focused on aboveground crop evaluations.  However, the root system is also an extremely important part of the crop condition to evaluate.  
 
Root systems were described in a basic manner in a recent article on 2 May 2023 (UA Vegetable IPM Newsletter Volume 14, No. 9).  
 
The effective root zone depth is the depth of soil used by the bulk of the plant root system to explore a soil volume and obtain plant-available moisture and plant nutrients.  Effective root depth is not the same as the maximum root zone depth. As a rule of thumb, we commonly consider about 70% of the moisture and nutrient uptake by plant roots takes place in the top 24 inches of the root zone; about 20% from the third quarter; and about 10% from the soil in the deepest quarter of the root zone (Figure 1).  
 
The small and very fine root hairs are the most physiologically active portion of a developing root system.  It is important that the plants continue to develop and generate fresh young roots and an abundance of fine root hairs to maintain water and nutrient uptake.

Figure 1.  General pattern for plant-water and nutrient uptake from the soil profile. 

It is important to point out that these general root development patterns are dependent on the nature of the soil profile in the fields.  Soil profiles with compaction layers, as well as rock or caliche layers will limit root development and full exploration of the soil volume that the plants are capable of (Figure 2).

Figure 2.  Generalized soil profile with major horizons.

Therefore, in scouting fields and making crop evaluations, examining the root systems is an important part of the process.  Leafy green vegetable crops need to develop a marketable plant in a relatively short amount of time and a strong root system is essential.  
 
It does take more time and effort to check root systems and it is a plant destructive process since we need to literally excavate the roots.  So, it is also important to be careful of where and how we sample plants and the root systems in a field.
 
Crop species can vary significantly in their patterns of root development and it is important to know what is “normal” when evaluating crops in the field.  An excellent reference for vegetable crop root system development is a 1927 publication by Dr. John E. Weaver and William E. Bruner from the University of Nebraska (Root Development of Vegetable Crops).  This publication can be found at the following link:
 
https://soilandhealth.org/wp-content/uploads/01aglibrary/010137veg.roots/010137toc.html
 
A few basic examples from the Weaver and Bruner publication are provided in the following figures (Figures 3-10).

Figure 3.  Cauliflower, 3 weeks after transplanting.



Figure 4.  Cabbage roots, 55 days after transplanting.



Figure 5.  Cabbage roots, 75 days after transplanting.



Figure 6.  Pepper roots, 24 days.



Figure 7.  Pepper roots, 45 days (6 weeks).



Figure 8.  Pepper roots, mature.



Figure 9.  Lettuce roots, 3 weeks.  The roots on the right were grown in compact soil, the roots on the
left were grown in loose/open soil.



Figure 10.  Lettuce roots, 60 days.

This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches between bed centers. All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

It’s October and planting season is well underway. When planting lettuce, uniform seed spacing is critical for efficient, economical crop thinning. Due to their lack of precision, automated lettuce thinning machines cannot eliminate lettuce plants that are spaced closer than about 1 1/8” apart. These closely spaced plants, commonly referred to as “doubles”, must be carefully removed by hand which is time consuming and expensive.

Several years ago, we conducted trials examining the influence of planter travel speed on seed spacing uniformity (Siemens and Gayler, 2016). In the study, two types of planters - a vacuum planter (Stanhay 785 Singulaire) and a belt planter (Stanhay 870) were tested with pelleted lettuce seed at travel speeds of 1.0, 1.5, 2.0 and 2.5 mph at the Yuma Agricultural Center. Vacuum planter test results showed that the percentage of “difficult to thin” spacings, defined seeds spaced less than 1.1” apart, increased from about 5% to 10% as speed increased from 1.0 mph to 2.5 mph (Fig. 1). Concomitantly, the percentage of seeds “precisely placed” within 0.5” of the target location (i.e., 2.0 ± 0.5”) decreased from 70% to less than 45%, and the percentage of skips increased from 7% to 30%. Variability of seed spacing uniformity as measured by the coefficient of variation (COV) of seed spacings also increased.

Similar declines in planter performance were found with the belt planter (Fig. 2). As travel speed increased from 1.0 to 2.5 mph, the percentage of difficult to thin spacings increased from 2% to 10%, precise spacings decreased from 93% to 65% and skips increased from 2% to 8%.

For both planter types, there was a significant decline in performance as speed increased from 1.5 mph to 2.0 mph, a difference in speed of only 0.5 mph. These results suggest that it is prudent to check planter performance at the chosen operating speed prior to establishing an entire block to ensure that seed spacing uniformity, not just the number of seeds per foot, is acceptable.

In short, the study showed that planter travel speed had a significant effect on seed spacing uniformity and difficult to thin, close spacings - the higher the speed, the poorer the performance.

You may be asking what is the reason for the phenomenon observed? A logical explanation is that seeds are traveling at the speed of the planter when they are released and tend to “bounce and roll” in the direction of travel when they hit the soil surface. Thus, the higher the travel speed, the further seeds bounce and roll resulting in increased seed spacing variability.

References

Siemens, M.C., & Gayler, R.R. (2016). Improving seed spacing uniformity of precision vegetable planters. Appl. Eng. Agric., 32(5), 579-587

Fig. 1. Seeding performance of a vacuum vegetable planter sowing lettuce when
operated at four travel speeds.


Fig. 2. Seeding performance of a belt vegetable planter sowing lettuce when operated at
four travel speeds

Sprinkler irrigation systems are delivering water throughout the Yuma CO. Either for germination or chemigations in lettuce, broccoli, onion and spinach.
How are you handling the absence of Dacthal (DCPA) in your operations?
One strategy that worked good in onions at the Gila Valley for one of our PCAs this week was the application of Prefar (bensulide) at 6qt. The weed complex he has included Purslane (Portulaca oleracea), Pigweed (Amaranthus palmeri), and is expecting later germination of Lambsquarter (Chenopodium album), Gooseofot (Chenopodium murale), and London Rocket (Sisymbrium irio). Control looks great and scouting the field in untreated areas we noticed there was a seedbank that could have caused a problematic infestation of purslane. The Pest Control Advisor is planning to include Goal (oxyfluorfen) in his weed control program later. 
We all know bensulide is an old treatment and many of you are using it, but our friend PCA wanted to share his experience just in case some of us have the same weeds.
If you would like to share with the Ag. community some of your experiences or new strategies used successfully, email the IPM Team. Also, please let us know if you like include a treatment or see a product tested in the onion and broccoli herbicide trials we are starting at the Experiment Station.
 
Following are links to some articles on onion weed control:
 
https://ag.arizona.edu/crop/vegetables/weeds/Dacthal.html
 
https://escholarship.org/content/qt91w4d06x/qt91w4d06x.pdf?t=lnryxp&v=lg
 
https://repository.arizona.edu/bitstream/handle/10150/221477/370100-165-167.pdf
 
https://ipm.ucanr.edu/agriculture/onion-and-garlic/herbicide-treatment-table/

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased considerably y in the past 2 weeks and about average for late summer
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Wellton) particularly near alfalfa
 
Cabbage looper:         
Cabbage looper numbers remain low consistent previous years.
 
Diamondback moth:      
DBM moths were not caught in any trap since June; average for this time of the year.
 
Whitefly:                      
Adult movement decreased in past 2 weeks consistent with previous years
 
Thrips:                         
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity has highest in Wellton and Dome Valley, and slightly above average for early August